1. Field of the Invention
The present invention relates to solid-state imaging devices and, more particularly, to an amplifying type solid-state imaging device in which a fixed pattern noise (FPN) can be canceled from a video signal formed from a pixel (i.e., pixel signal).
2. Description of the Related Art
FIG. 1 of the accompanying drawings shows an example of a conventional amplifying type solid-state imaging device.
As shown in FIG. 1, MOS (metal oxide semiconductor) transistors Qe, Qe, . . . , each having an annular-shaped gate, form pixels. The MOS transistors Qe, Qe, . . . are arranged in a matrix of rows and columns (i.e., in a two-dimensional fashion). Each of the MOS transistors Qe, Qe, . . . , has an annular-shaped gate. A drain provided at the outside of the annular-shaped gate of the MOS transistor Qe is connected to a power supply (V.sub.DD line) and a source provided at the inside of the annular-shaped gate of the MOS transistor Qe is connected to signal lines. The annular-shaped gate of the MOS transistor Qe is connected to vertical scanning lines. The annular-shaped gate is made of thin transparent polysilicon, and a channel current of the MOS transistors Qe, Qe, . . . is modulated by photoelectrically converting light incident on the channel through the angular-shaped gate. Horizontal switching transistors Qh, Qh, . . . , are connected between signal lines associated with vertical columns of pixels and an output line in order to effect the horizontal scanning.
A vertical scanner (vertical scanning circuit) 1 is adapted to scan horizontal rows of the pixels that are arranged in a matrix fashion. A horizontal scanner (horizontal scanning circuit) 2 is adapted to control the horizontal switching transistors Qh, Qh, . . . A signal of a pixel which belongs to the horizontal row scanned by the vertical scanner 1 and which belongs to the column scanned by the horizontal scanner 2 is output to the exterior as an output signal of the amplifying type solid-state imaging device.
An analog-to-digital (A/D) converter 3 is provided exteriorly of the amplifying type solid-state imaging device. The A/D converter 3 converts an output pixel signal from the amplifying type solid-state imaging device into a digital signal. A frame memory 4 is adapted to store therein one frame of the output signal from the A/D converter 3. More specifically, the frame memory 4 stores therein one frame of the output signal from the A/D converter 3 in order to cancel a noise signal (fixed pattern noise). In the following description of the present invention, the fixed pattern noise will be referred to hereinafter as "FPN" for simplicity.
A subtracter 5 subtracts the signal (noise signal) output from the frame memory 4 from the digital signal (pixel signal) output from the A/D converter 3.
In the conventional solid-state imaging device shown in FIG. 1, the frame memory 4 stores therein one frame of a pixel signal (corresponding to an FPN signal, i.e., noise signal) obtained when the entire amplifying type solid-state imaging device is shielded from light from the outside. If the pixel signal is normally output from the A/D converter 3 when light becomes incident on the amplifying type solid-state imaging device, then the noise signal of the pixel of the pixel signal is read out from the frame memory 4 and the FPN is canceled by subtracting the noise signal from the pixel signal of the same pixel by the subtracter 5.
FIG. 2 is a schematic diagram showing an arrangement of another example of the conventional amplifying type solid-state imaging device.
As shown in FIG. 2, in this amplifying type solid-state imaging device, the FPN that occurred in the pixel Tr is canceled by CDS (correlated double sampling) circuits 20 provided between the horizontal switching transistors Qh and the signal lines. Also, the FPN generated by the CDS circuit 20 is canceled by subtracting the FPN from the pixel signal. As shown in FIG. 2, the frame memory 4 shown in FIG. 1 is replaced with a line memory 4a. The line memory 4a stores therein as a noise signal an optical black signal of one horizontal line portion in a vertical optical black row (not shown) during a vertical optical blanking period.
The amplifying type solid-state imaging device shown in FIG. 1 requires that the frame memory 4 have a storage capacity large enough to store therein the noise signal of one frame. Furthermore, this solid-state imaging device requires that the A/D converter 3 to digitize the output pixel signal so that the output pixel signal may be stored in the frame memory 4. There is then the problem that the amplifying type solid-state imaging device cannot be made inexpensive. Furthermore, there is the problem that the noise signal of one frame should be stored in the frame memory 4 each time the cameraman takes a picture.
The amplifying type solid-state imaging device shown in FIG. 2 requires that the line memory 4a have a storage capacity of one horizontal line amount though this storage capacity of the line memory 4a is not as large as that of the frame memory 4. The amplifying type solid-state imaging device shown in FIG. 2 also requires the A/D converter 3 and therefore cannot be made inexpensive satisfactorily. Furthermore, although the amplifying type solid-state imaging device shown in FIG. 2 need not store the noise signal (unlike the amplifying type solid-state imaging device shown in FIG. 1), and since the noise signal is automatically written in the line memory 4a at every frame so as to cancel the FPN, the amplifying type solid-state imaging device shown in FIG. 2 has the problem that FPNs which are different at every pixel cannot be canceled out completely, because FPNs of all horizontal lines are canceled by the optical black signal of one horizontal line regardless of the fact that FPNs have subtle differences at every horizontal line.
Furthermore as the related art, U.S. Pat. No. 4,914,519 describes, a photoelectric-conversion apparatus has sample and hold circuits which sample and hold a signal read out from the same photoelectric converting element, and a refreshed remaining signal and a noise is canceled by effecting a subtraction on the above two signals.